High voltage current transformer



July 15, 1969 R. L. BERG 3,456,222

HIGH VOLTAGE CURRENT TRANSFORMER Filed April 25. 1968 INVENTOR.

ROBERT L. BERG: BY [AZQMM ATTORNEY United States Patent 3,456,222 HIGH VOLTAGE CURRENT TRANSFORMER Robert L. Berg, Broomail, Pan, assignor to General Electric Company, a corporation of New York Filed Apr. 25, 1968, Ser. No. 724,125 Int. Cl. I-Itllf 27/02 U.S. (ll. 336-92 6 Claims ABSTRACT OF THE DISCLOSURE Discloses a high voltage current transformer comprising a grounded tank comprising a top plate and a cup-shaped body portion detachably connected thereto. A tubular insulator is mounted on the top plate; and the primary winding passes through the tubular insulator into the tank and then back through the insulator. The secondary structure is located within the tank around the primary Winding. The secondary structure is hung from the top plate by a suspension mounting that comprises a frame mechanically supporting said secondary structure and means for securing the frame to the top plate independently of the cup-shaped body portion.

This invention relates to a high voltage current transformer and, more particularly, relates to improved means for mounting the usual cores and secondary windings of the transformer.

The type of current transformer that I am concerned with comprises a grounded tank, an insulating column mounted atop the tank, and a high voltage primary conductor comprising a loop portion within the tank and spaced apart arms extending from opposite ends of the loop portion through the tubular insulator to terminals at the top of the insulator. The usual cores and secondary windings are located within the tank with the cores surrounding the loop-shaped portion of the primary conductor.

For assembling the cores about the primary conductor and for inspecting and adjusting this assembly, it has been customary to provide a large access opening in the tank through which the cores could be inserted or removed. Despite the large size of this opening, however, accessibility has still been rather limited and diificulties have been encountered in performing all the nec essary adjustments, inspections and assembly operations.

An object of my invention is to construct the current transformer in such a manner that improved access can be had to the structure within the tank to facilitate assembly, inspection, and adjustment.

Another object is to construct the current transformer in such a manner that most of the tank can be of a light-Weight, inexpensive construction.

In carrying out the invention in one form, I construct the current transformer tank from a top plate and a cup-shaped body portion detachably connected thereto. Mounted on the top plate is the usual vertically-extending tubular insulator. The primary winding comprises two spaced-apart conductive arms extending through the tubular insulator and a loop-shaped conductor within the tank electrically interconnecting the arms. A core within the tank surrounds the loop-shaped primary conductor in spaced relationship thereto, and .a secondary winding also located within the tank is wound about the core. The core and secondary winding are hung from said top plate by a suspension mounting that comprises a frame mechanically supporting said core and secondary winding and means for .securing said frame to the top plate independently of said cup-shaped body portion. Upon detachment from the top plate, the cup-shaped body portion can be lowered to expose the parts within 3,456,222 Patented July 15, 1969 "ice the tank without disturbing the suspension mounting of the core and secondary winding on the top plate.

For a better understanding of the invention, reference may be had to the following description taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a sectional side elevational view of a high voltage current transformer embodying one form of the invention.

FIG. 2 is a sectional view along the line 2-2 of FIG. 1.

FIG. 3 is a sectional view of the secondary structure and-its associated supported shield.

Referring now to FIG. 1, the high voltage current transformer shown therein comprises a grounded metal tank 12 comprising a metal top plate 14 and a cup: shaped body portion 15 having an upwardly-facing mouth across which the top plate 14 extends. The body portion is detachably connected to the top plate by suitable means, such as screws 16, extending through openings in the top plate and threaded into a flange 18 on the body portion.

Mounted on the top plate 14 is a vertically extending tubular insulating column 20, preferably of porcelain. This tubular column 20 has an annular flange 21 suitably bonded to its lower end and bolted to the top plate 14. An opening 23 in the top plate 14 is disposed in alignment with the bore of the tubular insulating column 20.

The primary conductor of the current transformer comprises two spaced-apart conductive arms 30 and 31 extending through the tubular insulator 20 into the tank 15. In the preferred embodiment illustrated, one arm 30 is a tubular member and the other 31 is a rod coaxially. disposed within the tubular member 30. The primary conductor further comprises a loop-shaped conductor 32 located within the tank and electrically interconnecting the lower ends of the conductors 30 and 31. The illustrated loop-shaped conductor 32 is a generally tubular member comprising two upper portions 32a and 32b each detachably connected to a lower portion 320 by suitable means, such as screws 34 located within the tubular member. Upper portion 32a is electrically and meehanically connected to inner conductive arm 31, and

upper portion 32b is electrically and mechanically con-' nected to outer conductive arm 30. Suitable local insulation (not shown) is provided between portions 32a and 32b for forcing all the current flowing through these parts to follow a path around the loop-shaped conductor via portion 320. It will be apparent that the current path for all the primary current extends through the series combination of conductive arm 31, -loop-shaped conductor 32, and conductive arm 30.

At the top of the insulating column 20, there are spaced apart primary terminals 36 and 38 connected to the conductors 30 and 31, respectively. Through these terminals primary current enters and leaves the current transformer. Terminal 36 is a metal plate extending across the top of the insulating column 20 and suitably secured thereto. The tubular conductive arm 30 is suitably clamped to this metal plate 36. The other conductive arm 31 is also clamped to plate 36 and is electrically insulated therefrom by an insulating member 40. Thus, the two conductive arms 30 and 31 are mechanically supported by the plate 36.

The detailed construction of the primary conductor and the terminals is not a part of my invention. This construction is described in more detail and claimed in copending application Ser. No. 724,126, Stewart, filed Apr. 25, 1968, and assigned to the assignee of the present invention.

In the illustrated embodiment, two current transformer secondary windings 40 and 42 are shown within tank 12. It is to be understood, however, that any number of such windings could be provided, depending upon the intended application of the current transformer. Each of the secondary windings and 42 is of a conventional descign, and, as such, is wound about its own annular magnetic core 44, which encompasses the loop-shaped primary conductor 32 is spaced-apart relationship there to. The turns of each of these windings are electrically insulated from each other and from the core in a conventional manner. The cores 44 are at ground potential, as is one point on each of the secondary windings.-

For supporting the cores and secondary windings, a U-shaped frame, or cradle, is provided. This cradle 50 comprises a pair of spaced-apart vertically extending legs 52 and a generally semi-cylindrical saddle, or bight, portion 54 secured at its respective opposite ends to these legs. Preferably, the legs 52 and the saddle portion 54 are made of a suitable metal and are welded together. A shim 56 of insulating material rests on the saddle portion 54, and the cores with their windings 40 and 42 rest on shim 56.

For attaching the secondary structure 40, 42, 44 to the cradle 50, a pair of horizontally-spaced flexible bands 60 are provided. Each of these bands 60 extends around the outside, or bottom, of the saddle portion 54, through suitable openings 62 in the saddle portion 54, and around the top of the annular secondary structure 40, 42, 44. The opposite ends of each band 60 are suitably attached together, as by a clip 63, so that the band firmly holds the secondary structure which it encircles against the shim 56 and cradle 50. A suitable spacer 66 of insulating material is interposed between the top of the secondary structure and the bands 60 to protect the insulating coating on the secondary winding.

The secondary structure is enclosed by grounded metal shielding 70 that serves to electrostatically shield the secondary structure by preventing concentrations of electrical stress adjacent the irregular surfaces thereof. In this regard, the metallic shielding 70 is of a generally toroidal form with a smoothly curved external surface to reduce stress concentrations thereadjacent. Preferably, shield 70 is made of two generally semi-toroidal components 71 and 72 respectively disposed on opposite sides of the secondary structure and connected together by suitable straps 73 at the outer periphery of the toroidal shield. Suitable insulation 74 is provided between the two parts of the shield to prevent the shield from forming a short circuited turn about cores 44. The shield 70 also comprises a generally semicircular band 76 covering the top portion of the two semi-toroidal components and providing additional electrical shielding for any irregular surfaces in this region.

Shield 70 and windings 40 and 42 are at substantially ground potential, but suitable electrical insulation is provided between them to maintain electircal isolation between the secondary winding circuits and the conductive shield 70. A pair of leads of the secondary windings are shown at 78 in FIG. 1. These extend between the secondary windings and a suitable terminal plate 80 in the vertical wall of the tank 14. Suitable plug connections 79 are provided to permit the leads to be readily detached from the terminal plate 80. For convenience in illustration, this terminal plate is shown in the position of FIG. 1, but in an actual embodiment, it is located in a position displaced 90 degrees around tank 12 from that of FIG. 1 so that the leads 78 are remote from the high voltage primary 32 and are shielded therefrom by cradle leg 52.

For further modifying the electrostatic field distribution to prevent undesirable stress concentrations, an addiitonal electrostatic shield 84 is provided. Shield 84 is a tubular metal member surrounding the primary conductor in spaced relationship thereto in the region where the primary conductor passes through top plate 14. This shield 84 is supported from and electrically connected to the top plate 14.

The entire current transformer is supported from top plate 14 on a suitable framework, portions of which are illustrated at 86 and 87. When it is desired to gain access to the parts inside of tank 12, the screws 16 are removed, and the cup-shaped portion 15 of the tank is lowered, thereby exposing the parts inside the tank. After the cupshaped portion 15 of the tank has been partially lowered, the plugs 79 for the secondary leads can be detached from the terminal plate to permit continued lowering to take place without interference from the leads.

It is to be noted that the above-described disassembly of the tank 12 can take place without any need for disturbing the secondary structure 40, 42, 44. Since the U-shaped cradle 50 supports the secondary structure from the top plate independently of the cup-shaped body portion 15 of the tank, the secondary structure remains in its normal position undisturbed by removal of cup-shaped tank portion 15.

Similarly when the current transformer is being assembled, the secondary structure is mounted within cradle 50 before the cup-shaped tank portion 15 is in place. Any required adjustments of the secondary structure can then be made under conditions of almost complete accessibility with respect to the secondary structure. Thereafter, the cup-shaped tank portion 15 can be lifted into position and attached to the top plate with assurance that these adjustments will not be disturbed by the body portion 15.

It will be apparent that top plate 14 supports the remainder of the current transformer assembly without reliance on the bottom portion 15 of the tank. Thus, most of the usual forces developed or imposed upon the current transformer are transmitted to the supporting framework 86, 87 without passing through the body portion 15 of the tank. This permits the body portion to be of a simpler, lighter weight design than has been typical of comparable prior current transformers.

For some current transformers it may be desirable to provide a minor amount of additional or auxiliary support for the secondary structure, particularly during shipment of the transformer. Such auxiliary support means is shown near the bottom of tank 12, where a lug 90 welded to cradle 50 is shown projecting downwardly therefrom. When the cup-shaped tank body 15 is in position, an L-shaped bracket 92 is attached between lug 90 and the bottom wall of the tank. Access for attaching this bracket 92 is made available through a small hand-hole 94 in the bottom of the tank. The bracket has suitable slots therein for receiving the fastening screws to facilitate its being fastened in place without affecting the position of lug 90 or the parts connected thereto. After bracket 92 is attached, the hand-hole is covered by a suitable cover 95, held in place by means not shown.

The auxiliary attaching means 90, 92 is optional in many current transformer applications and can be omitted in such applications. Its main purpose is to assure that the internal parts of the current transformer will not be affected by mechanical shocks encountered during shipment.

For insulating the grounded structure of the current transformer from the high voltage primary conductor, a suitable gaseous insulation is provided within tank 12 and hollow insulating column 20. This gaseous insulation 18 preferably sulphur hexafiuoride at a pressure of several atmospheres. Pressure-tight joints throughout the assembly prevent any significant leakage of pressurized gas from the assembly. Although I prefer to use a pressurized gas as the insulating medium, the invention in its broader aspects is also applicable to liquid-filled current transformer assemblies.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be Patent of the United States is:

What I claim as new and desire to secure by Letters 1. A high voltage current transformer comprising:

(a) a grounded tank comprising a metal top plate and a cup-shaped body with an upwardly-facing mouth detachably connected to said top plate,

.(b) a vertically-extending tubular insulator mounted on said top plate,

(c) a primary winding comprising two spaced-apart conductive arms extending through said tubular insulator and a loop-shaped conductor within said tank electrically interconnecting the lower ends of said arms,

(d) a core located within said tank and surrounding said loop-shaped conductor in spaced relationship .thereto,

(e) a secondary winding located within said tank and linked to said core,

(f) and means for suspending said core and secondary winding from said top plate comprising: a frame mechanically supporting said core and secondary winding and means for securing said frame to said top plate independently of said cup-shaped tank body,

(g) said cup-shaped tank body, upon detachment from said top plate, being lowerable to expose the parts inside said tank without disturbing the suspension' mounting of said core and secondary Winding on said top plate.

2. The current transformer of claim 1 in which:

(a) said frame is a generally U-shaped structure having a pair of spaced apart legs and a bight portion interconnecting said legs at their lower ends,

(b) said means for securing said frame to said top plate comprises means connecting said legs at their upper ends to said top plate,

(c) and said core is supported on said bight portion.

3. The current transformer of claim 2 in which a band extends around said core and part of said bight portion to hold said core in place against said bight portion.

4. The current transformer of claim 1 in which an auxiliary support is detachably connected between said frame and the bottom portion of said tank body.

The current transformer of claim 1 in which an auxiliary support is detachably connected between said frame and the bottom portion of said tank body, and an access-hole is provided in said tank body near said auxiliary' support to provide access for attachment or detachment of auxiliary support.

6 The current transformer of claim 1 in which said topplate serves to support said tubular insulator and said tank body portion when said tank body portion is attached to said top plate and serves to support said tubular insulator, said primary and secondary windings, and said'core after said tank body portion is detached from said'top top plate.

References Cited UNITED STATES PATENTS 2,331,106 10/1943 Camilli 336-173 XR 1,573,077 2/1926 McClintock 336- XR 3,097,346 7/1963 Horelick et a1. 33692 XR 3,380,009 4/1968 Miller 33694 XR LEWIS H. MYERS, Primary Examiner T. I. KOZMA, Assistant Examiner U.S. Cl. X.R. 3 3 6-84, 174 

